Constant delivery positive displacement pump



March 1965 M. D. BENNETT ETAL 3,172,353

CONSTANT DELIVERY POSITIVE DISPLACEMENT PUMP Original Filed Dec. 5, 19572 Sheets-Sheet l March ,1965 M. D. BENNETT ETAL 3,172,363

CONSTANT DELIVERY POSITIVE DISPLACEMENT PUMP Original Filed Dec. 5, 19572 Sheets-Sheet 2 INVENTORS 4/4AV/A 0 BIA W577 United States PatentOfifice 3,172,363 Federated Mar. 9, 1965 3,172,363 tIONd'lANT DELIVERYEQfil'i.

DlSPLACElr WNT IPUMP Marvin D. Bennett, Manhattan Beach, and Richard D.

Bennett, Pasadena, fialitl, assignors, by mesne assignrnents, to Royalindustries, inc, Pasadena, Calii, a corporation of California Griginalapplication Dec. 5, i957, Ser. No. 790,894, new Patent No. 3,ll77,204,dated Feb. 12, 1963. Divided and this application Nov. 30, 1962, Ser.No. 242,578

8 Qlaims. (til, 163-9 This invention relates generally to positivedisplacement pumps and more particularly to a positive displacement pumpdesigned to produce substantially constant fiuid delivery.

This application is a division of our co-pending application bearingSerial No. 700,894, filed on December 5, 1957, now Patent No. 3,077,204,and assigned to the sin e assignee as the present application.

Constant delivery fluid pumps find useful application in many fields.One field in which the pumps of this character are presently employed toadvantage is the construction field wherein it is now relatively commonpractice in the construction field to apply cement and plaster tobuilding surfaces by spraying. T he invention will be described withreference to the pumping of such material. it will become clear as thedescription proceeds, however, that the present pump is capable ofgeneral application and can be used for pumping any type of fluid orfluid-like material.

It a relatively uniform layer of plaster or cement material is to beapplied to a building surface, the rate of flow of material from thespray nozzle of the spray unit must be relatively constant. This, inturn, requires a constant delivery pump capable of producingsubstantially constant rate of material flow to the spray nozzle.

Constant delivery pumps are, of course, known in the art. Most of theseprior pumps, however, were deficient in that they were limited in thekind of material they could successfully pump, wer prone to wear,required power plants of excessive size, or did not produce trulyconstant fluid flow.

A broad object of the present invention is the provision of a new andimproved constant delivery pump.

A more specific object is the provision of a constant delivery, positivedisplacement pump.

Another object is the provision of a constant delivery, positivedisplacement pump which requires only a relatively small power plant.

A further object is the provision of a constant delivery, positivedisplacement pump which is capable of pumping a wide variety of fluidsand fluid-like materials and is ideally suited to the pumping of plaser,cement, and other abrasive materials.

Yet a further object is the provision of a constant delivery, positivedisplacement pump embodying ii.- proved valve means and means foreffecting compensation for ditierent compressibilities of materials tobe pumped.

A still further object is the provision of a constant delivery, positivedisplacement pump which produces substantially constant fluid delivery,which is adjustable to vary the rate of uniform delivery, and which isrelatively simple in construction, inexpensive to manufacture, andimmune to maloperation.

Briefly, the foregoing and other objects are achieved by the provisionof a of communicating piston pump units. During operation, a first pumpunit receives material to be pumped from a supply and delivers thematerial to the cylinder or the second pump unit.

The strokes of the units are timed so that the second pump unitundergoes its suction stroke during the delivery stroke of the firstpump unit. The displacement of the second pump unit is somewhat lessthan that of the first pump unit.

During each delivery stroke of the first pump unit, a portion of thematerial pumped remains in the second pump unit and the remainder of thematerial flows to the discharge of the pump. During the suction strokeor" the first pump unit, the second pump unit undergoes its deliverystroke and delivers the remainder of the material, delivered by thefirst pump unit during its previous delivery stroke, to the discharge ofthe pump.

The exact timing of the pump units compensates for valve closure timeand other factors. A substantially constant flow of material to thedischarge of the pump is thereby maintained.

A better understanding of the invention may be had from the followingdetailed description taken in connection with the annexed drawings,wherein:

FIG. 1 is a view in perspective of an improved plaster pump and the likewhich embodies the invention;

FIG. 2 illustrates the operating means for one of the two pump units ofthe pump of FIG. 1;

FIG. 3 illustrates the operating means for the other pump unit of thepump of FIG. 1;

FIG. 4 is a top plan view of the operating means of FIG. 3;

FIG. 5 is a diagram illustrating the operation of the pump of FIG. 1;

FIG. 6 is a top plan View, partially in section, of the pump with partsomitted for the sake of clarity;

FIG. 7 is a detail in section illustrating certain check valve meansshown in FIG. 6 in a second position of operation;

FIGS. 8 and 9 are enlarged sections illustrating the valve meansembodied in the present pump; and

FIG. 10 illustrates a modified check valve.

Referring now to the drawings, the illustrated constant delivery pumpwill be seen to comprise a frame 16 of any suitable design. Mounted onthis frame is a hopper T12 for receiving a charge of material to bepumped. The pump illustrated is especially designed to pump plaster andcement materials.

Indicated at 14 is a first, or main, piston pump unit. This unitincludes a cylinder 16 having an inlet 18. This inlet has an intakepassage 18 communicating to the hopper l2 and to the adjacent end ofcylinder 16. Pump unit 14 also has a discharge passage 17. Positionedwithin the inlet 18 is the new and improved one-way check valve 2i)(FIG. 6). This valve, which will be presently described, allows flow ofmaterial into the cylinder 16 through the inlet 18 but blocks flow inthe reverse direction.

Movable in the cylinder 16 is a piston 22 having a piston rod 24. Rod 24is connected to the lower end of an arm 25, the upper end of which ispivoted on a cross shaft 25a on frame it). An intermediate point of arm25 is pivotally connected through a telescopically adjustable link 26 toa crank 27a on a disc 27. Disc 27 is journalled on a terminallythreaded, axial stud 28a projecting from the center of a circular flange28 rigid on one end of a shaft 29 journalled on frame 10. Disc 27 isretained on the stud 28a by a nut, as shown. Fric tionally received inaligned holes in the disc and flange is a pin 30 which is sheared underexcessive pumping loads to prevent damage to the equipment.

Shaft 29 is driven from a motor 31 to cause reciprocation of the piston22; in the cylinder 16. Disc 27 is removable by removing its securingnut for replacement by another disc having a crank pin 27a with adifferent effective crank arm, for reasons to be seen.

Mounted on the frame it) is a second piston pump unit 32. This secondpump unit includes an inlet conduit 34 through which extends the intakepassage 34' for the latter unit. Conduit 34 is connected to the firstpump unit 14 in such a way that intake passage 34 communicates with thedischarge passage 17 of the first pump unit. Disposed in the conduit 34is a second oneday check valve 36 identical to the one-way valve 20.Valve 36 permits fiow from the pump unit 14 to the pump unit 32 butblocks fiow in the reverse direction.

Second pump unit 32. includes a cylinder 38 in which is movable a piston4d. Piston 4%) includes a rod 42, one end of which is pivotally attachedto one end of an arm 44. The other end of arm 44 is pivoted on crossshaft 250. Pump 32 is provided with approximately twothirds of thedisplacement of pump 14 either by making the diameter of cylinder 38less than that of cylinder 16 or by making the stroke of pump 32 lessthan that of pump 14.

Arm 44 journals an adjustable cam follower roller 46 which bears againsta cam 48 removably keyed to the shaft 29. Roller 46 is adjustable alongthe arm to adjust the point of contact of the roller with cam 48. Cam 4%is thus rotated in synchronism with crank arm 27a and is operative tocause movement of the piston 40 to the left in its cylinder 38. Theleft-hand end of the cylinder 38 has an outlet 5%) adapted forconnection to a discharge hose 52, for example. The discharge passage 50of the second pump unit extends through this outlet 50. This hoseterminates in nozzle (not shown). Cam 48 is removable for reasons to beseen.

Referring now to FIGS. 6 and 7 as well as FIGS. 8 and 9, illustratingvalve it; in enlarged detail, the numeral 56 denotes an elastic checkvalve member in the form of a rubber ball. Ball 56 is contained in acylindrical housing 58. Housing 58 has a passage extending therethroughwhich is formed witha reduced inlet portion bore 69 opening into anenlarged passage portion or chamber 62. Extending across the bore 69 arecross pins 64- which act as stops to limit left-hand travel of the ball56 in bore 60.

Bore 6% has a diameter approximately the same as or just slightly lessthan the diameter of ball 56, while the diameter of chamber 62 issubstantially larger than ball 56. Plus 66 act as stops to limitright-hand movement of ball 56 in chamber 62. From this description itwill be seen that ball 56 is movable from bore 6% into chamber 62 inresponse to flow to the right through the valve. The clearance betweenthe ball and the wall of chamber 62 provides a flow space about theball.

When flow in the opposite direction occurs through the valve, ball 56 isforced into the bore 69 and against the cross pins 54 at the left-handend of the bore. Axial pressure on the ball causes radial expansion ofthe latter against the wall of bore 60 to form a seal, as shown in FIG.9. During movement of ball 56 into the bore 69, the wall of the latteris wiped clean by the ball (FIG. 8) so as to permit an efficient seal tobe formed. Valve 36 is identical to valve 24 just described.

The illustrated valve is highly desirable for the use described since itis less prone to wear and accomplishes a liquid tight seal even withgranular and abrasive materials, such as plaster and cement.Conventional check valves are not suitable for these latter materialsinasmuch as any particles of the material on the seat of the check valvewould prevent the latter from completely closing. During the pumpingstroke, therefore, water in the material will be squeezed out past theslightly unseated check valve. This results in instantaneous setting ofthe material in the valve and jamming of the latter.

Operation of the illustrated pump thus far described is as follows.Assumin the hopper 12 to contain a charge of material to be pumped suchas moist plaster or cement, each right-hand suction stroke of the piston22 in the primary pump unit 14 draws material into the cylinder 16 fromthe hopper 12. This material is pumped from the cylinder 16 throughconduit 34 to the second pump i unit 32 during the left-hand pumpingstroke of the piston 22. A portion of this material flows into cylinder3% of the second pump unit.

The material entering the cylinder 38 of the second pump unit 32 exertsa force on the piston 40 tending to move the latter to the right andforce the roller 46 on arm 44 against the cam 43. As will be presentlymore fully described, the shape of the cam 48 is such as to allowcontrolled right-hand movement of piston 40 under the action of thisforce during the delivery stroke of the primary pump unit.

The parts are so proportioned that during this delivery stroke of theprimary pump unit, a portion of the material delivered to the secondpump unit is absorbed by right-hand movement of the piston 44 Theremainder of the delivered material flows through the discharge 50 ofthe second pump unit to the hose 52.

During each suction stroke of the primary pump unit, the piston 40 ofthe second pump unit 32 is forced to the left by the cam 48. Thispumping stroke of the second pump unit displaces the material remainingin the latter unit after the previous delivery stroke of the primarypump unit. Thus, during each delivery and suctio'n stroke of the primarypump unit 14, a portion of the material pumped by the latter pump unitis discharged through the discharge 5% of the second pump unit.

The second pump unit 32, therefore, in effect evens out the surges inthe flow of the material from the first pump unit 14 so as to maintain asubstantially uniform delivcry of material to the pump discharge 5% andhose 52. The manner in which this action is accomplished in the presentpump will now be described in greater detail by reference to the daigramof FIG. 5.

In FIG. 5 curve A represents the pulsating flow of material delivered bythe first pump unit 19 to the second pump unit 32, the area under thecurve, of course, indicating the volume of material pumped. Thereference point a on the curve denotes the start of the delivery strokeof the first pump unit at which time the pump piston 22 is at theextreme right-hand limit of its previous suction stroke.

Under ideal conditions, curve A would conform approximately to a sinewave since the piston 22 is driven in approximately simple harmonicmotion. In practice with compressible materials, however, the initialportion of curve A between points a and b is distorted, as shown. Thisis due first to the time required to close the inlet check valve 29 andopen the discharge check valve 36, which valves are, of course, closedand opened, respectively, at the start of the pumping stroke of thefirst pump unit, and second to the fact that the material in the firstpump unit must be initially compressed a certain amount before it willstart to fiow from the first pump unit to the second pump unit.

These delays introduced by valve operations and material compressioncause the fiow from the first pump unit to the second pump unit duringthe first portion of the pumping stroke of piston 22 to remain zero fora short period of time, then increase slowly, and finally rise rapidlyto point b on the curve. During the remainder of the pumping stroke,flow of material from the first pump unit is approximately sinusoidal,as indicated by the curve A between point I) and c.

From point c to point a at the start of its next delivery stroke, thepiston 22 undergoes its suction stroke so that no material is deliveredby the first pump unit.

Curve B represents the operating cycle of the second pump unit 32. Aspreviously mentioned, this pump unit has approximately two-thirds of thedisplacement of the first pump unit and is operated by the cam 48 in amanner to maintain a substantially uniform delivery of material to thedischarge 5% of the pump.

Thus, as earlier indicated, the piston 40 in the second pump will havebeen operated through its pumping stroke by the cam 48 during thesuction stroke of the first pump unit just preceding the pumping strokeof the latter unit indicated by the curve A in FIG. 5. Cam 48 is soshaped that during the terminal portion of said pumping stroke of thesecond pump unit, which is denoted by the portion c] of curve B, andwhich will .be observed to overlap the initial portion of the pumpingstroke of the first pump unit, the total volumetricrate of materialdelivered by the action of the two pump units to the pump discharge 50remains substantially uniform and approximately equal to one-third ofthe maximum volumetric rate of material delivery produced by the firstpump unit. This maximum delivery, of course, occurs at point g on curveA. Line C denotes one-third this maximum rate.

Referring to FIG. 2, illustrating the cam 48 in detail, the portion e-f'of the cam surface 48' is shaped to accomplish the controlled pumpingaction of the second pump unit occurring between points e and f on curveB. At point 1, on curve B, the piston 40 in the second pump unit is atthe end of its pumping stroke, while the first pump unit is stillundergoing its pumping stroke and delivering material at rate C. Curve Bbetween points 1 and h thereon denotes the suction stroke of the secondpump.

The material delivered by the first pump unit to the second pump unitduring this suction stroke of the latter, of course, exerts .a force onthe piston 40 tending to move the latter to the right, as viewed in FIG.6. The cam surface 48', between points f'-h' thereon is shaped to permitcontrolled movement of the piston 40 to the right under the action ofthis force in such manner that the excess material delivered by thefirst pump, from point i to point 1' of curve A remains in the secondpump unit and the remainder of the delivered material flows to thedischarge 50. The rate of discharge from the pump during this period,therefore, remains substantially uniform at :the value C.

At point h on curve B the second pump unit reverses and commences itspumping stroke under the action of the cam 48. This occurs at point 1'of curve A whereat the first pump is again delivering at the rate C.Since the output of the first pump unit now drops below the line C, thesecond pump unit must deliver its retained charge of material at such arate as to just olfset the decrease in material flow from the first unitand thereby maintain a uniform delivery to the pump discharge.

A certain volume of material delivered by the second pump unit is usedto effect closure of the check valve 36. This closure occurs betweenpoints h and k on curve B. If the delivery of pump unit 32 was notmomentarily increased during this period, therefore, the rate of discharge fi'om the pump would drop off momentarily, as indicated by thedotted line curve between points h and k on curve B. To prevent this,cam surface 48' is formed with a relaitvely abrupt rise between points hand k which causes, during the above period, increased delivery of thesecond pump unit sufficient to maintain the effective delivery from thesecond pump unit and, therefore, from the pump discharge 50,substantially uniform at the volumetric rate C.

From point k to point I on curve B, the output of pump unit 32 is againcaused to be approximately sinusoidal so that the combined delivery ofboth pump units remains uniform at the rate C. The delivery of thesecond pump unit during this period is effected by portion k-l' of thecam surface 48'.

Between points I and point e of the cam surface 48', the latter isshaped to effect a substantially constant volumetric rate of deliveryfrom the second pump unit equal to the rate C. During this period, ofcourse, the first pump unit is undergoing its suction stroke so that nomaterial is delivered thereby. The above cycle is then repeat-ed.

Clearly then, the volumetric discharge rate from the pump, denoted bythe line C, remains substantially uniform[ In the use of the illustratedpump for spraying cement, plaster, and other similar materials, it isdesirable to vary the output of the pump for different jobs. Thus, whenspraying a finish plaster coat, the rate of delivery of the pump ispreferably less than for heavy base coats.

Adjustment of the pump output may be accomplished by replacing the crankplate 27 by one having a different effective crank arm for its crank pin27a, and replacing the cam 48 by a similarly shaped cam which alter thetotal stroke of the second pump unit to fit the new stroke of the firstpump unit.

Moreover, materials of the type under discussion have differentcompresison ratios. This difference in compression ratios of differentmaterials, of course, will alter the shape of the curve A (FIG. 5)between points a and b there-on, that is, a greater or lesser portion ofthe pumping stroke of the first pump unit will be consumed incompressing the material to a point where actual delivery of thematerial to the second pump unit starts.

To maintain the output of the pump constant, of course, the output ofthe second pump unit must be varied accordingly during this period.Different compression ratios of material will, of course, also eifectthe output of the second pump unit at the start of its pumping stroke,i.e., between points h and k on curve B.

To this end, the cam 48 is removable for replacement by a cam which isconfigured to suit the particular material to be pumped. Thus, severalcams may be provided for selective mounting on the pump, each cam beingdesigned for a particular material or materials whose compression ratiosfall within a particular range.

Compensation for a change in the compression ratio from one material toanother may also be accomplished by adjusting the travel of the ball 56in the check valves 20 and 36 of the invention, as illustrated in FIG.10. In this figure the numeral denotes a sleeve formed with the inletbore 69, which is slidab-le in the valve housing 58'. This sleeve mountsthe cross pins 64 which limit movement of the ball 56 in the bore 60.

Sleeve is adjusted in the axial directions indicated by a threaded shaft102 operable exteriorly of the housing 58. This adjustment of the sleevehas the effect of varying the travel of the hall 56 during closure ofthe valve and hence the volume of material necessary to effect closureof the valve.

In use, when a material to be pumped has less compressibility than theparticular material tor which the cam 48 is designed, the sleeve 100will be shifted to the lefit, as viewed in FIG. 10, to increase thetravel of the ball 56. This has the efliect of increasing the travel ofthe pump piston necessary to close the valve and hence compensating forthe lesser travel of the piston required to compress the material. Withmaterials having greater compressibility, of course, the sleeve 1100 isadjusted in the opposite direction.

Numerous modifications in design and arrangement of parts of theinvention are possible Within the scope of the following claims.

What is claimed is:

1. In a constant delivery pump comprising a frame, a first piston pumpunit on said frame including a first cylinder, a first piston movable inthe cylinder, and a first intake and a first discharge passage openingto one end of the cylinder, a second piston pump unit on said frame ofsmaller displacement than said first unit and including a secondcylinder, a second piston movable in the cylinder, a second intakepassage opening to one end of the second cylinder and communicating withsaid first discharge passage, and a second discharge passage opening tosaid one end of the second cylinder, and valve means in said firstintake passage and in said communicating passages for permitting flow ofmaterial to be pumped into said first cylinder through said first intakepassage and from said first cylinder to said second cylinder throughsaid communicating passages, and blocking flow of said material in thereverse direction through said first intake passage and communicatingpassages, a rotary driving shaft on said frame, a connection betweensaid shaft and first piston for reciprocating the latter in its cylinderas the shaft rotates to effect an intermittent pumping action of thefirst unit, said connection including adjustable means for varying thestroke of the first piston, the second piston being movable in onedirection in its cylinder by the pressure developed by the pumpingaction of the first unit, a rotary cam separate from said connection,means releasably connecting said cam to said shaft for rotation by thelatter, and cam follower means engaging a limited portion of the surfaceof said cam and operatively connected to the second piston for movingthe latter piston in the opposite direction in its cylinder andcontrolling the movement of the latter piston in said one direction inits cylinder as the shaft rotates, said cam surface having an irregularprofile for effecting movement of said second piston in predeterminedtime relationship with respect to movement of the first piston, and saidcam being removable from said shaft for replacement by a cam having acam surface of different profile matching the adjusted stroke of thefirst piston.

2. In a constant delivery pump comprising a frame, a first piston pumpunit on said frame including a first cylinder, a first piston movable inthe cylinder, and a first intake and a first discharge passage openingto one end of the cylinder, a second piston pump unit on said frame ofsmaller displacement than said first unit and including a secondcylinder, a second piston movable in the cylinder, a second intakepassage opening to one end of the second cylinder and communicating withsaid first discharge passage, and a second discharge passage opening tosaid one end of the second cylinder, and valve means for permitting flowof material to be pumped into said first cylinder through said firstintake passage and from said first cylinder to said second cylinderthrough said communicating passages, and blocking flow of said materialin the reverse direction through said first intake passage andcommunicating passages, a rotary driving shaft on said frame, aconnection between said shaft and first piston for reciprocating thelatter in its cylinder as the shaft rotates to effect an intermittentpumping action of the first unit, the second piston being movable in onedirection in its cylinder by the pressure developed by the pumpingaction of the first unit, a rotary cam separate from said connection,means releasably connecting said cam to said shaft for rotation by thelatter, andcam follower means engaging a limited portion of the surfaceof said cam and operatively connected to the second piston for movingthe latter piston in the opposite direction in its cylinder andcontrolling the movement of the latter pistonin said one direction inits cylinder as the shaft rotates, said cam surface having an irregularprofile for effecting movement of said second piston in predeterminedtimed relationship with respect to movement of the first piston, saidcam being removable from said shaft for replacement by a cam having acam surface of different profile to permit adjustment of the stroke ofthe second piston to compensate for different compressibilities ofmaterials to be pumped.

3. In a constant delivery pump comprising a frame, a first piston pumpunit on said frame including a first cylinder, a first piston movable inthe cylinder, and a first intake and a first discharge passage openingto one end of the cylinder, a second piston pump unit on said frame ofsmaller displacement than said first unit and including a secondcylinder, at second piston movable in the cylinder, a second intakepassage opening to one end of the second cylinder and communicating withsaid first discharge passage, and a second discharge passage opening tosaid one end of the second cylinder, and valve means in said firstintake passage and in said communicating passages for permitting flow ofmaterial to be pumped into said first cylinder through said first intakepassage and from said first cylinder to said second cylinder throughsaid communicating passages, and blocking flow of said material in thereverse direction through said first intake passage and communicatingpassages, a rotary driving shaft on said frame, a connection betweensaid shaft and first piston for reciprocating the latter in its cylinderas the shaft rotates to effect an intermittent pumping action of thefirst unit, the second piston being movable in one direction in itscylinder by the pressure developed by the pumping action of the firstunit, a rotary cam separate from said connection driven by said shaft, acam follower arm pivoted at one end to said frame, operatively connectedat its other end to said second piston and mounting a camfollowerelement engaging a limited portion of the cam surface for movingthe latter piston in the opposite direction in its cylinder andcontrolling the movement of the latter piston in said one direction inits cylinder as the shaft rotates, said cam surface having an irregularprofile for effecting movement of said second piston in predeterminedtimed relationship with respect to movement of the first piston, andmeans for adjusting the position of said cam follower element on saidarm to shift the point of contact of the element with said cam surface.

4. A method for continuously spraying moist compressible materials suchas plaster, concrete, mortar, and the like at a substantially uniformspray rate including the steps of introducing the moist material into apumping unit, compressing the moist material in the pumping unit apreselected amount Without substantially altering the moisture contentof the material to cause the material to flow in a stream, discharging apreselected portion of the flowing material from said pumping unit at asubstantially uniform spray rate, temporarily storing the remainder ofthe discharged material in another pumping unit while maintaining itunder compression and discharging same during a preselected period, aportion of which discharge period coincides with the discharge of thematerial from the first pumping unit whereby a continuous discharge ofthe material at a substantially uniform rate is provided.

5. In a constant delivery pump for moist compressible materials such asplaster, concrete, mortar, and the like comprising a frame, means forstoring a preselected quantity of the compressible material to be pumpedmounted on said frame, a first pumping unit mounted on said frame,conduit means including first control means communicating with saidstorage means and said pumping unit to allow the material to be pumpedto be controllably passed to said pumping unit, said control means beingre sponsive to a reduced pressure created by said pumping unit to allowthe material to be pumped to charge the pumping unit and to be closed inresponse to the pumping of the material, a second pumping unit mountedon said frame, a discharge outlet, second conduit means including secondcontrol means communicating with said first and second pumping units anda discharge outlet, said second control means being responsive to thereduced pressure created by said first pumping unit to close the secondconduit means to said second pumping unit and the discharge outlet andto open the second conduit means in response to the pumping of thematerial by said first pumping unit to allow the material to flow to thesecond pumping unit and the discharge outlet, and drive means mounted onthe frame for operating the first and second pumping units in atimed-overlapping, pumping sequence to cause a continuous discharge ofthe material at the discharge outlet at a substantially uniform rate.

6. In a constant delivery pump of the type of claim 5 wherein said firstand second control means comprise elastic ball check valves.

7. In a constant delivery pump of the type of claim 5 wherein the firstand second pumping units comprise piston and cylinder units and saidsecond unit is of a smaller displacement than said first unit.

8. A constant delivery pump for moist, compressible, heavy-bodiedmaterials having an initial compressibility and then acting asessentially incompressible to thereby flow in a stream when pumpedcomprising first and second pumping units, means for alternatelycharging the first and second pumping units with said material to bepumped, conduit means including a discharge outlet communicating witheach of said pumping units to allow the charged material to bedischarged by said pumping units through the discharge outlet in astream, and controllable drive means for alternately driving the firstand second pumping units to discharge the materials through thedischarge outlet, each of said pumping units being effective forinitially compressing the material therein to cause the material to flowin a stream, the controllable drive means including means for operatingthe first and second pumping units in a timed overlapping dischargesequence to compensate for the initial action of compressing saidmaterial in each of the pumping units to maintain a continuous flow ofthe material at a substantially uniform rate through the dischargeoutlet.

References Cited in the file of this patent UNITED STATES PATENTS111,293 Windhausen J an. 24, 1871 1,261,061 Seymour Apr. 2, 19182,281,767 Heckert May 5, 1942 2,424,750 Heckert July 29, 1947 2,448,104Longenecker Aug. 31, 1948 2,702,008 Stockard Feb. 15, 1955 2,819,835Newhall Jan. 14, 1958 2,858,767

Smith Nov. 4, 1958

1. IN A CONSTANT DELIVERY PUMP COMPRISING A FRAME, A FIRST PISTON PUMPUNIT ON SAID FRAME INCLUDING A FIRST CYLINDER, A FIRST PISTON MOVABLE INTH CYLINDER, AND A FIRST INTAKE AND A FIRST DISCHARGE PASSAGE OPENING TOONE END OF THE CYLINDER, A SECOND PISTON PUMP UNIT ON SAID FRAME OFSMALLER DISPLACEMENT THAN SAID FIRST UNIT AND INCLUDING A SECONDCYLINDER, A SECOND PISTON MOVABLE IN THE CYLINDER, A SECOND INTAKEPASSAGE OPENING TO ONE END OF THE SECOND CYLINDER AND COMMUNICATING WITHSAID FIRST DISCHARGE PASSAGE, AND A SECOND DISCHARGE PASSAGE OPENING TOSAID ONE END OF THE SECOND CYLINDER, AND VALVE MEANS IN SAID FIRSTINTAKE PASSAGE AND IN SAID COMMUNICATING PASSAGES FOR PERMITTING FLOW OFMATERIAL TO BE PUMPED INTO SAID FIRST CYLINDER THROUGH SAID FIRST INTAKEPASSAGE AND FROM SAID FIRST CYLINDER TO SECOND CYLINDER THROUGH SAIDCOMMUNICATING PASSAGES, AND BLOCKING FLOW OF SAID MATERIAL IN THEREVERSE DIRECTION THROUGH SAID FIRST INTAKE PASSAGE AND COMMUNICATINGPASSAGES, A ROTARY DRIVING SHAFT ON SAID FRAME, A CONNECTION BETWEENSAID SHAFT AND FIRST PISTON FOR RECIPROCATING THE LATTER IN ITS CYLINDERAS THE SHAFT ROTATES TO EFFECT AN INTERMITTENT PUMPING ACTION OF THEFIRST UNIT, SAID CONNECTION INCLUDING ADJUSTABLE MEANS FOR VARYING THESTROKE OF THE FIRST PISTON THE SECOND PISTON BEING MOVABLE IN ONEDIRECTION IN ITS CYLINDER BY THE PRESSURE DEVELOPED BY THE PUMPINGACTION OF TH FIRST UNIT, A ROTARY CAM SEPARATE FROM SAID CONNECTION,MEANS RELEASABLY CONNECTING SAID CAM TO SAID SHAFT FOR ROTATION BY THELATTER, AND CAM FOLLOWER MEANS ENGAGING A LIMITED PORTION OF THE SURFACEOF SAID CAM AND OPERATIVELY CONNECTED TO THE SECOND PISTON FOR MOVINGTHE LATTER PISTON IN THE OPPOSITE DIRECTION IN ITS CYLINDER ANDCONTROLLING THE MOVEMENT OF THE LATTER PISTON IN SAID ONE DIRECTION INITS CYLINDER AS THE SHAFT ROTATES, SAID CAM SURFACE HAVING AN IRREGULARPROFILE FOR EFFECTING MOVEMENT OF SAID SECOND PISTON IN PREDETERMINEDTIME RELATIONSHIP WITH RESPECT TO MOVEMENT OF THE FIRST PISTON, AND SAIDCAM BEING REMOVABLE FROM SAID SHAFT FOR REPLACEMENT BY A CAM HAVING ACAM SURFACE OF DIFFERENT PROFILE MATCHING THE ADJUSTED STROKE OF THEFIRST PISTON.